Emilio Segre Italian physicist Date of Birth: 01.02.1905 Country: Italy

Biography of Emilio Segre

Emilio Gino Segre, an Italian-American physicist, was born in Tivoli, a small town near Rome. He was one of the three sons of industrialist Giuseppe Segre and Amelia (nee Treves) Segre. Emilio initially attended primary school in Tivoli and completed his secondary education at the Mamiani High School in Rome in 1922. Before pursuing physics, which had interested him since childhood, he studied engineering at the University of Rome for five years. His transition to specializing in physics was partly influenced by Enrico Fermi, who was teaching at the university at that time. Segre and Fermi became close friends and colleagues, and Segre successfully defended his doctoral dissertation in physics in 1928 under Fermi's guidance. After graduating from university, Segre served four years of compulsory military service in the Italian army as an artillery officer before returning to the University of Rome as an instructor in physics. He received a fellowship from the Rockefeller Foundation, which allowed him to work with Otto Stern in Hamburg and Peter Zeeman in Amsterdam. Subsequently, Segre became an adjunct professor in Fermi's department. Prior to his military service, Segre had been involved in atomic spectroscopy, molecular beams, and X-ray radiation. He conducted important research in the field of spectroscopy of forbidden lines and the Zeeman and Stark effects. The Zeeman effect refers to the splitting of lines into several components in an external magnetic field, while the Stark effect (named after Johannes Stark) involves the splitting of lines under the influence of an electric field. Later, Segre became interested in nuclear physics. Alongside Fermi and other colleagues, he became a pioneer in the field of neutron physics. Fermi's group irradiated various materials with neutrons and in 1935, they obtained slow neutrons, which had their speed reduced due to collisions with light nuclei. Slow neutrons later played an important role in nuclear energy production, as target nuclei have a higher probability of capturing slow neutrons and undergoing nuclear reactions compared to fast neutrons. In 1936, Segre was appointed Dean of the Faculty of Physics at the University of Palermo. In the same year, he made his first visit to the United States, where he worked on the cyclotron at the University of California, Berkeley. For some time, he attempted to discover the element with atomic number 43 (43 protons in the nucleus) - a gap in the periodic table between molybdenum (42) and ruthenium (44). In Berkeley, Ernest O. Lawrence provided Segre with a sample of molybdenum bombarded with deuterons (hydrogen nuclei with one neutron added to the proton). Upon returning to Italy, Segre and his colleagues subjected the sample to thorough chemical analysis. Their work was successful, and they managed to identify traces of the element with atomic number 43. Segre named it technetium, derived from the Greek word technetos (artificial), as it was the first element obtained artificially. Technetium, which proved to be a valuable therapeutic agent in medicine, does not occur naturally on Earth but has been detected spectroscopically in stars. Segre made his second visit to Berkeley in 1938. In collaboration with Dale R. Corson and Kenneth R. MacKenzie, he synthesized the artificial element with atomic number 85 (filling another gap in the periodic table), which was named astatine. In 1940, Segre, along with Glenn T. Seaborg and other colleagues, discovered plutonium-239 (with atomic number 94). In the summer of 1938, the Italian government passed anti-Semitic laws regarding civil rights, and Segre, who was Jewish and a long-time opponent of the regime, decided to stay in the United States. As a research assistant in the Radiation Laboratory at Berkeley, Segre continued his research on artificial radioactivity and nuclear isomerism (the existence of nuclei with the same number of protons and neutrons but in different energy states, thus possessing different nuclear properties). Working with Seaborg, Segre developed an effective chemical method for separating nuclear isomers. In 1944, he obtained American citizenship. The discovery of plutonium-239 had unforeseen consequences, as the new element turned out to be fissile. Starting in 1944, large quantities of plutonium were synthesized. Plutonium became the primary source of energy in the atomic bomb dropped on Nagasaki, Japan in August 1945. After the war, during which Segre served as the head of a group at the Los Alamos Laboratory of the Manhattan Project (a top-secret organization tasked with developing the atomic bomb), he returned to Berkeley as a full professor. His subsequent research on elementary particle physics, conducted with his characteristic enthusiasm, earned him a well-deserved reputation as one of the pioneers of modern physics in both theory and experiment. In the early 1950s, Segre began collaborating with Owen Chamberlain in an effort to produce and detect a new particle called the antiproton, whose existence had been theoretically predicted (the antiproton is the negatively charged counterpart of the positively charged proton, possessing opposite properties). More than 20 years earlier, P.A.M. Dirac had predicted the existence of the positron - the positively charged counterpart of the well-known electron - based on the mathematical symmetry of relativistic quantum theory. In 1932, Carl D. Anderson reported the discovery of this particle in cosmic rays - high-energy radiation from extraterrestrial sources. Anderson's discovery stimulated the search for other antiparticles. Using accelerators designed to reach the appropriate energies, physicists discovered the existence of the antimeson, an analog of the meson (a particle with mass intermediate between that of an electron and a proton). However, the energies achievable with existing accelerators were not sufficient for the birth of the antiproton. Those energies became accessible after the construction of the Bevatron (an accelerator capable of accelerating particles to energies in the billions of electron volts) in Berkeley. The Bevatron was partly designed with the anticipation of experiments with the antiproton. Segre, Chamberlain, and their colleagues accelerated protons to an energy of 6.2 billion electron volts and directed them at copper atoms. According to theory, antiprotons should be produced at this energy. Physicists expected antiprotons to be relatively rare, short-lived (as they would quickly interact with protons and annihilate), and extremely difficult to detect among the many other subatomic particles produced in high-energy collisions. A major achievement of Segre, Chamberlain, and their team was the development of a clever method for detecting and unmistakably identifying particles that had previously eluded researchers. The experimenters used a complex system of magnets and focusing magnetic devices to select particles with the predicted mass, negative charge, and specific velocity. Electronic counters and timers were used to measure the passage of particles over a predetermined distance. Finally, photographic emulsions were used to capture the annihilation of protons and antiprotons for final confirmation. To prevent erroneous results, the experimenters employed other measures as well. Annihilation events produced star-like tracks, indicating that incoming antiprotons, upon colliding with protons, disappeared and gave birth to approximately five mesons per annihilation event. After accumulating a sufficient amount of convincing data, the scientists announced in 1955 the experimental confirmation of the existence of antiprotons. The experiment also revealed that antiprotons are not produced individually but in proton-antiproton pairs (similar to how positrons are born in electron-positron pairs). In 1959, Segre and Chamberlain were awarded the Nobel Prize in Physics "for the discovery of the antiproton." According to Erik Hultén, a member of the Royal Swedish Academy of Sciences, who spoke at the award ceremony, "There is now nothing that is better known or clearer than the process of pair creation and annihilation." Following the receipt of the Nobel Prize, Segre continued his research in elementary particle physics at Berkeley until his retirement in 1972. Two years later, he was appointed as a professor of nuclear physics at the University of Rome, and in 1975, as an emeritus professor at the same university. In 1936, Segre married Elfride Spiro, and they had three children together: a son and two daughters. His wife passed away in 1970, and two years later, he remarried Rosa Mines. Segre was a talented popularizer of physics and published a biographical study, "Enrico Fermi, Physicist" (1970), among other books. He was an avid fisherman and mountaineer. Segre received the August Wilhelm von Hofmann Medal from the German Chemical Society (1958) and the Stanislao Cannizzaro Prize from the Italian National Academy of Sciences (1958), among other awards. He was a member of the National Academy of Sciences, the Italian National Academy of Sciences, the American Philosophical Society, the American and Italian Physical Societies, the American Academy of Arts and Sciences, the Indian Academy of Sciences, the Heidelberg Academy of Sciences, the Uruguayan Scientific Society, and the National Academy of Sciences of Peru. Segre was awarded honorary degrees by the University of Palermo, San Marcos University (Lima), Tel Aviv University, and Gustavus Adolphus College.